The boil-off gas (BOG) compressor is one of the most critical pieces of equipment in the handling of boil-off gas from liquefied natural gas (LNG). It ensures the safety of the transportation and receiving systems of LNG. This study used a three-dimensional finite element model to investigate the heat transfer process in the cylinder of a BOG compressor. The results showed that when the BOG compressor was running steadily, the average temperatures of the suction chamber and the discharge chamber were similar to-109 degrees C and similar to-60 degrees C, respectively. The temperature of the compression chamber was between these two values. Simulations of the temperature of the inner surface of the cylinder showed that more than 60% of the total temperature drop occurred within the first ten minutes of the compressor's operation, and that the largest temperature difference between various parts of the cylinder also occurred during this period. Thereafter, the temperature gradually decreased until it reached a dynamically stable state. Finally, it was proven that temperature fluctuation only existed on the inner surface of the cylinder and that its amplitude was lower than 0.003 degrees C. Accordingly, the global temperature can be regarded as invariable. (C) 2012 Elsevier Ltd. All rights reserved.